80 ASSIMILATION IN CARNIVORA. 



the greater part of the earth of bones is obtained by 

 the direct assimilation of phosphate of lime, Avhile 

 the soluble phosphates are better adapted for the 

 l^roduction of nervous matter. 



In the graminivora, therefore, whose food con- 

 tains so small a proportion of phosphorus or of 

 phosphates, the organism collects .all the soluble 

 phosphates produced by the metamorphosis of tis- 

 sues, and employs them for the developement of the 

 bones and of the phosphorised constituents of the 

 brain ; the organs of excretion do not separate these 

 salts from the blood. The phosphoric acid which, 

 by the change of matter, is separated in the uncom- 

 bined state, is not expelled from the body as phos- 

 phate of soda ; but we find it in the solid excre- 

 ments in the form of insoluble earthy phosphates. 



XVI. If we now compare the capacity for in- 

 crease of mass, the assimilative power in the grami- 

 nivora and carnivora, the commonest observations 

 indicate a very marked difference. 



A spider, which sucks with extreme voracity the 

 blood of the first fly, is not disturbed or excited by 

 a second or third. A cat will eat the first, and per- 

 hajis the second mouse presented to her, but even 

 if she kills a third, she does not devour it. Exactly 

 similar observations have been made in regard to 

 lions and tigers, which only devour their prey when 

 urged by hunger. Carnivorous animals, indeed, re- 

 quire less food for their mere support, because their 



